TDA5250D2_07 INFINEON [Infineon Technologies AG], TDA5250D2_07 Datasheet - Page 41

• Manufacturer Part Number: TDA5250D2_07
• Description: ASK/FSK 868MHz Wireless Transceiver
• Manufacturer: INFINEON [Infineon Technologies AG]

Measured Magnitude of S11 of evalboard:
Figure 3-3
Above you can see the measured S11 of the evalboard. The –3dB-points are at 810MHz and
930MHz. So the 3dB-bandwidth is:
The loaded Q of the resonant circuit is:
The unloaded Q of the resonant circuit is equal to the Q of the inductor due to its losses.
An approximation of the losses of the input matching network can be made with the formula:
The noise figure of the LNA-input-matching network is equal to its losses. The input matching
network is always a compromise of sensitivity and selectivity. The loaded Q should not get too high
because of 2 reasons:
more losses in the matching network and hence less sensitivity
Data Sheet
Loss
Q
Q
B
U
L
=
=
=
=
−
f
Q
U
20
f
INDUCTOR
center
−
B
∗
f
log
L
S11 measured
=
=

 

1
≈
930
868
120
−
36
Q
Q
3 ,
MHz
@
U
MHz
L
MHz

 

868
=
−
MHz
−
810
20
=
7
∗
MHz
2 .
log



1
=
−
120
7
36
2 .
MHz



41
=
2
dB
[3 – 4]
[3 – 1]
[3 – 3]
[3 – 2]
TDA5250 D2
Version 1.7
Application
S11_measured.pcx.
2007-02-26